Comparison of methods for detoxification of spruce hydrolysate for bacterial cellulose production

Abstract

BackgroundBacterial cellulose (BC) is a nanostructured material with unique properties and wide applicability. In order to decrease the production cost of bacterial cellulose, lignocellulose-based media have considerable potential as alternative cost-effective feedstocks. However, pretreatment and enzymatic hydrolysis of lignocellulose to sugars also generate fermentation inhibitors. Detoxification of lignocellulosic hydrolysates is needed to achieve efficient production of BC. In this investigation, different methods for detoxification of spruce hydrolysate prior to production of BC were compared with respect to effects on potential inhibitors and fermentable sugars, sugar consumption, BC yield, and cell viability. The objectives were to identify efficient detoxification methods and to achieve a better understanding of the role played by different inhibitors in lignocellulosic hydrolysates.ResultsIn a first series of experiments, the detoxification methods investigated included treatments with activated charcoal, alkali [sodium hydroxide, calcium hydroxide (overliming), and ammonium hydroxide], anion and cation ion-exchange resins, and reducing agents (sodium sulfite and sodium dithionite). A second series of detoxification experiments included enzymatic treatments (laccase and peroxidase). The potential inhibitors studied included aliphatic acids, furan aldehydes, and phenolic compounds. The best effects in the first series of detoxification experiments were achieved with activated charcoal and anion exchanger. After detoxification with activated charcoal the BC yield was 8.2 g/L, while it was 7.5 g/L in a reference medium without inhibitors. Treatments with anion exchanger at pH 10 and pH 5.5 gave a BC yield of 7.9 g/L and 6.3 g/L, respectively. The first series of experiments suggested that there was a relationship between the BC yield and phenolic inhibitors. Therefore, the second series of detoxification experiments focused on treatments with phenol-oxidizing enzymes. The BC yield in the laccase-detoxified hydrolysate reached 5.0-5.5 g/L after 14 days cultivation, which demonstrated the important inhibitory role played by phenolic compounds.ConclusionsThe investigation shows that detoxification methods that efficiently remove phenolics benefit bacterial growth and BC production. Negative effects of salts could not be excluded and the osmotolerance of Gluconacetobacter xylinus needs to be further investigated in the future. Combinations of detoxification methods that efficiently decrease the concentration of inhibitors remain as an interesting option.

Development of an Energy Biorefinery Model for Chestnut (Castanea sativa Mill.) Shells

“…Several procedures have been described for the removal of inhibitory compounds from LB hydrolyzates in order to limit their negative action on the fermentation [34]. Among these, the extraction with ethyl acetate [35], ion exchange [36], AC adsorption [37] or biological treatments with microorganisms and enzymes [38] can be referred. The treatment with AC is considered an effective method for the removal of phenolic compounds from LB hydrolyzates because of the large surface area of the charcoal particles, high adsorption capacity, and availability [36].…”

“…Among these, the extraction with ethyl acetate [35], ion exchange [36], AC adsorption [37] or biological treatments with microorganisms and enzymes [38] can be referred. The treatment with AC is considered an effective method for the removal of phenolic compounds from LB hydrolyzates because of the large surface area of the charcoal particles, high adsorption capacity, and availability [36]. In addition, because some of these potential inhibitory molecules possess strong antioxidant power, their subsequent desorption from charcoal enables the recovery of bioactive compounds that can be further utilized for value-added applications [18,28,30,33,39].…”

Detoxification of a Lignocellulosic Waste from a Pulp Mill to Enhance Its Fermentation Prospects

“…As will be seen further in Section 3.6, detoxification with BC or AC seems to be adequate working with yeasts or bacteria because of the high removals of LS, phenolics and acetic acid. This research gave better results in case of furfurals and weak acids in comparison with Guo et al [17] and Lee et al [22] who removed 94%-96% of furfurals, 14%-28% of acetic acid or 88% of total phenolics.…”

“…The experimental results obtained in this paper together with the fermentation requirements of a specific microorganism permit to establish the detoxification possibilities that might be implemented in different case studies. It should be noted that the study cases represented in Figure 5b belong to hydrolyzates similar to the industrial liquors used in this work such as hardwood hydrolyzates [22,46], softwood hydrolyzates [9,17] and spent sulfite liquors [19,23,35,47]. Main SSL inhibitors can be classified into weak acids, furan derivatives and phenolics among others [48,49].…”

“…In recent years, many publications have studied a single detoxification technique coupled with a specific fermentation scenario [2,9,16,19,23,35]. Other papers have studied the combination of detoxification techniques experimentally [10,17,18,20,21,36,37] or from a theoretical viewpoint [26,31,38,39]. Nonetheless, the present research is the first paper working with spent sulfite liquor which compares different detoxification techniques showing which one of them would be adequate to produce seven different fermentation and value-added products (ethanol, bacterial cellulose, xylitol, polyhydroxyalkanoate (PHA), acetone-butanol-ethanol (ABE), succinic acid and polyhydroxybutyrate (PHB).…”